As indicated above, the best source of exact bore size would be Joel Etchen guns of course. But while I am not sure of the exact size (tho I bought one of these combos at the last Grand American), they use the Beretta 682 Gold E barrels, which are over bored. They are the Beretta "Optima" target bore, and use the Beretta Optima chokes (Beretta has three bore sizes: the Field "mobil choke bore, the field over bore "Optima Plus" choke system, and the target over bore "Optima" choke bore). Beretta lists the Optima bore size as 0.732